Phase-change-type heat spreader, flow-path structure, electronic apparatus,and method of producing a phase-change-type heat spreader

ABSTRACT

[Object] To provide a phase-change-type heat spreader, a flow-path structure, an electronic apparatus including the phase-change-type heat spreader, a flow-path structure used therein, and the like that are capable of improving a thermal efficiency by a phase change and lowering a thermal resistance. 
     [Solving Means] Capillary boards ( 401  to  404 ) in which a plurality of openings ( 408 ) penetrating the capillary boards are formed on a wall surface constituting grooves ( 405 ) in a longitudinal direction of the grooves ( 405 ), are laminated while each being rotated 90 degrees to be deviated within an X-Y plane so that the grooves ( 405 ) of those layers extend in mutually-orthogonal directions, and the plurality of openings ( 408 ) function as a part of a vapor-phase flow path through which a vapor refrigerant evaporated by heat received by a heat-receiving plate circulates.

TECHNICAL FIELD

The present invention relates to a phase-change-type heat spreader that receives heat from a heat source and diffuses the heat using a phase change of a working fluid, a flow-path structure used therein, an electronic apparatus including the phase-change-type heat spreader, and a method of producing a phase-change-type heat spreader.

BACKGROUND ART

From the past, there is a solid-type metal heat spreader as a device that absorbs and diffuses heat from a heat source. Such a solid-type metal heat spreader is thermally connected to, for example, a CPU (Central Processing Unit) of a PC (Personal Computer) and diffuses heat from the CPU. A heat sink, for example, is attached to the metal heat spreader, and heat is transferred to the heat sink from the metal heat spreader to be radiated in general.

In the solid-type metal heat spreader, however, there is a problem that, since a thermal diffusion efficiency depends on heat conductivity of metal, a response of the thermal diffusion is slow. Moreover, due to variations in a temperature within a thermal diffusion surface of the metal heat spreader, it is difficult to largely lower the temperature of the heat source.

To solve the problems as described above, there is conventionally proposed a phase-change-type heat spreader (see, for example, Patent Document 1). The heat spreader disclosed in Patent Document 1 is structured by laminating a heat-receiving plate (3), a heat-radiation plate (4), a thin groove plate (5), and a thick groove plate (6). The heat-receiving plate (3) receives heat from a heating element (2), and a refrigerant inside a closed vessel (1) is thus boiled. Vapors thereof mainly pass through grooves (6 a) of the thick groove plate (6), spread across the entire closed vessel (1), and are condensed on an inner wall surface of the closed vessel (1). The liquified refrigerant passes through grooves (5 a) of the thin groove plate (5) provided on the heat-receiving plate (3) to be supplied to a heat-receiving portion. By such a phase change of the refrigerant, heat is diffused across the entire heat spreader.

Patent Document 1: Japanese Patent

Application Laid-open No. 11-31768 (paragraph [0015], FIGS. 1 to 4)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the heat spreader of Patent Document 1, the grooves (6 a) through which a vapor refrigerant passes and the grooves (5 a) through which a liquid refrigerant passes are provided separately. In other words, the heat spreader is structured assuming that the vapors and liquid respectively pass through the grooves (6 a) and the grooves (5 a). However, when a thermal load by a heat source is large, the vapors also enter the grooves (5 a) for liquid. Since vapors have a property of temporarily expanding its volume, if the vapors enter the grooves (5 a) for liquid, the vapors continue to spread in the grooves (5 a). In this case, an amount of working fluid to be supplied is reduced to thus cause dryout.

In view of the circumstances as described above, it is an object of the present invention to provide a phase-change-type heat spreader, a flow-path structure, an electronic apparatus including the phase-change-type heat spreader, and a flow-path structure used therein, that are capable of improving a thermal efficiency by a phase change and lowering a thermal resistance.

It is another object of the present invention to provide a method of producing a phase-change-type heat spreader that can be produced with ease and has high reliability.

Means for Solving the Problems

For attaining the objects above, according to the present invention, there is provided a phase-change-type heat spreader diffusing heat using a phase change of a working fluid, including: a container (closed vessel) including a heat-receiving side and a heat-radiating side opposed to the heat-receiving side; a plurality of flow paths provided in the container while being laminated in a direction extending from the heat-receiving side to the heat-radiating side, each of the plurality of flow paths including a wall surface that causes the working fluid in a liquid phase to circulate by a capillary force; and a vapor-phase flow path that includes an opening and causes the working fluid in a vapor phase evaporated by heat received on the heat-receiving side to circulate so that the working fluid in the vapor phase moves toward the heat-radiating side via the opening, the opening penetrating the wall surface so that it is brought in communication with the plurality of flow paths.

In the present invention, a heat source is thermally connected to the heat-receiving side. The working fluid evaporates by the heat received on the heat-receiving side. The vapor-phase working fluid is circulated so as to move from the heat-receiving side to the heat-radiating side via the opening penetrating the plurality of flow paths. The vapor-phase working fluid is condensed when reaching a side close to the heat-radiating side, and the liquid-phase working fluid is circulated through the plurality of flow paths by a capillary force.

The present invention does not structurally separate the flow paths for the liquid-phase working fluid and the vapor-phase working fluid as in Patent Document 1. The present invention presupposes mixing of the vapor-phase working fluid and the liquid-phase working fluid and has been made based on a basic idea of controlling circulation directions of the working liquids.

The liquid-phase working fluid circulates through the plurality of flow paths within a plane between the heat-receiving side and the heat-radiating side, whereas the vapor-phase working fluid mainly circulates via an opening having a smaller flow-path resistance than the plurality of flow paths. Specifically, most of the evaporated vapor-phase working fluid moves substantially perpendicularly via the opening, and an amount of vapor-phase working fluid that passes through the plurality of flow paths is small, with the result that the circulation of the liquid-phase working fluid, that passes through the plurality of flow paths, can be prevented from being inhibited. Accordingly, a thermal efficiency by the phase change can be improved, and a thermal resistance can be lowered.

In the present invention, the vapor-phase flow path includes a condensation area in which the working fluid in the vapor phase is condensed, the condensation area being interposed between the heat-radiating side and the plurality of flow paths and being in communication with the plurality of flow paths via the opening. Accordingly, the vapor-phase working fluid that has passed through the opening from a side close to the heat-receiving side can be condensed in the condensation area, with the result that heat can be radiated efficiently.

In the present invention, the phase-change-type heat spreader further includes a return flow path through which the working fluid in the liquid phase that has been condensed in the condensation area returns to the plurality of flow paths. Typically, the return flow path is provided at a position relatively distant from a position at which a temperature of the heat source is highest (center of heat source) on the entire heat-receiving side of the container.

In the present invention, the condensation area includes a first flow-path layer including a plurality of first condensation flow paths that cause the working fluid to circulate in a first direction, and a second flow-path layer including a plurality of second condensation flow paths that cause the working fluid to circulate in a second direction different from the first direction and are in communication with the plurality of first condensation flow paths, the second flow-path layer being a layer different from the first flow-path layer in the direction extending from the heat-receiving side to the heat-radiating side. In other words, a first wall sectioning the first condensation flow paths and a second wall sectioning the second condensation flow paths are in different directions, and a columnar structure is thus formed at a portion at which the first wall and the second wall overlap. Accordingly, it is possible to secure a strength sufficient to endure a compression stress externally applied to the phase-change-type heat spreader.

For example, by bonding the first wall and the second wall by diffusion bonding, a strength sufficient to also endure a tension stress can be obtained. An example of the tension stress is a stress applied to the phase-change-type heat spreader at a time the working fluid evaporates inside the phase-change-type heat spreader and an internal pressure increases.

In the present invention, the plurality of flow paths include a first flow-path layer including a plurality of first flow paths that cause the working fluid to circulate in a first direction, and a second flow-path layer that includes a second flow path for causing the working fluid to circulate in a second direction different from the first direction and is a layer different from the first flow-path layer in the direction extending from the heat-receiving side to the heat-radiating side. Also in the present invention, the first wall sectioning the first flow paths and the second wall sectioning the second flow paths are in different directions, and a columnar structure is thus formed at a portion at which the first wall and the second wall overlap. Accordingly, it is possible to similarly secure a strength sufficient to endure an external compression stress. Moreover, also in the present invention, by bonding the first wall and the second wall by diffusion bonding, the same effect can be obtained regarding a strength with respect to a tension stress.

In the present invention, the opening of the vapor-phase flow path is provided plurally so that the plurality of openings are arranged in the direction in which the plurality of flow paths are laminated. Accordingly, it becomes easier for the vapor-phase working fluid to circulate via the plurality of openings in the direction in which the plurality of flow paths are laminated, with the result that a flow-path resistance of the vapor-phase flow path can be reduced.

In the present invention, the container includes on the heat-receiving side an inlet for the working fluid, an injection path that is in communication with at least one of the plurality of flow paths and the inlet, and a press area that is applied with a pressure on the heat-receiving side and blocks the injection path after the working fluid is injected into the plurality of flow paths via the inlet and the injection path, the phase-change-type heat spreader further including a columnar portion erected in the direction in which the plurality of flow paths are laminated at a position corresponding to the press area. Accordingly, when the working fluid is injected into the plurality of flow paths at a time the phase-change-type heat spreader is produced and the injection path is blocked by being pressed thereafter, a position above the columnar portion on the heat-receiving side is pressed. As a result, it is possible to prevent the plurality of flow paths and the vapor-phase flow path from being pressed by the press force to be blocked.

It is also possible to provide a dedicated press area above the injection path on the heat-receiving side so that the plurality of flow paths and the vapor-phase flow path are not formed at a position corresponding to the injection path. However, since the plurality of flow paths and the vapor-phase flow path are not provided at the position corresponding to such a dedicated press area, the press area is an area having a low thermal diffusion function. According to the present invention, since the plurality of flow paths and the vapor-phase flow path are disposed around the columnar portion, a thermal diffusion efficiency can be enhanced almost over the entire surface of the phase-change-type heat spreader.

The heat-radiating side may include the inlet and the injection path instead of the heat-receiving side.

In the present invention, a height of the plurality of flow paths in the direction in which the plurality of flow paths are laminated is 10 to 50 μm. With this structure, a capillary force optimal for the liquid-phase working fluid can be generated. If the height is smaller than 10 μm, a circulation amount of the liquid-phase working fluid is reduced to thus lower a thermal efficiency. If the height is larger than 50 μm, a desired capillary force does not act on the working fluid, and the thermal efficiency is thus lowered. In particular, in many cases, the present invention is typically applied to a case where the working fluid is pure water or ethanol.

In the present invention, the phase-change-type heat spreader further includes a first structural member constituting the plurality of flow paths and a second structural member constituting the vapor-phase flow path, and at least one of the container, the first structural member, and the second structural member is formed of copper.

According to another aspect of the present invention, there is provided a phase-change-type heat spreader diffusing heat using a phase change of a working fluid, including: a heat-receiving plate; a heat-radiating plate opposed to the heat-receiving plate; a plurality of first boards that each include a first groove for causing the working fluid in a liquid phase to circulate by a capillary force and an opening penetrating the first board so that the first grooves are brought in communication with one another and causes the working fluid in a vapor phase evaporated by heat received by the heat-receiving plate to circulate via the opening, the plurality of first boards being laminated in a direction extending from the heat-receiving plate to the heat-radiating plate; and a second board that includes a second groove for causing the working fluid in the vapor phase that has passed through the opening to circulate and is provided between the heat-radiating plate and the plurality of first boards.

In the present invention, a heat source is thermally connected to the heat-receiving plate. The working fluid evaporates by the heat received by the heat-receiving plate. The vapor-phase working fluid is circulated via the opening penetrating the first boards so that the first grooves are in communication with one another. The vapor-phase working fluid is condensed when reaching a side close to the heat-radiating plate, and the liquid-phase working fluid is circulated through the grooves by a capillary force.

Moreover, by setting the number of first boards as appropriate at a time the phase-change-type heat spreader is designed, an optimal phase-change-type heat spreader corresponding to an amount of heat generated by the heat source can be designed.

The second board may be provided plurally. In this case, the number of second boards only needs to be set in the same manner as in the case of setting the number of first boards.

According to the present invention, there is provided a flow-path structure used in a phase-change-type heat spreader that diffuses heat received by a heat-receiving plate using a phase change of a working fluid and includes the heat-receiving plate, a heat-radiating plate opposed to the heat-receiving plate, and a board including a groove that causes the working fluid in a vapor phase evaporated by the heat received by the heat-receiving plate to circulate, the flow-path structure being laminated between the heat-receiving plate and the board, the flow-path structure including: a plurality of ribs extending within a plane between the heat-receiving plate and the heat-radiating plate; and a wall surface that includes an opening penetrating the flow-path structure, for causing the working fluid in the vapor phase to circulate so that the working fluid in the vapor phase moves toward the heat-radiating plate, and causes the working fluid in a liquid phase to circulate by a capillary force, the wall surface being provided between the plurality of ribs.

According to the present invention, there is provided an electronic apparatus including a heat source and a phase-change-type heat spreader to diffuse heat from the heat source. The phase-change-type heat spreaders described above are used as the phase-change-type heat spreader.

According to the present invention, there is provided a method of producing a phase-change-type heat spreader, including: laminating a heat-receiving plate, a plurality of boards each including a groove for causing a working fluid to circulate, and a heat-radiating plate such that the plurality of boards are interposed between the heat-receiving plate and the heat-radiating plate; diffusion-bonding the heat-receiving plate, the plurality of boards, and the heat-radiating plate that have been laminated to thus form a flow path of the working fluid that corresponds to the grooves; injecting the working fluid into the grooves via an injection path for the working fluid, that is formed on the heat-receiving plate or the heat-radiating plate and is in communication with the flow path; and sealing up, after the injection of the working fluid, an inside of the flow path by blocking the injection path before connecting a heat source to the heat-receiving plate by reflow.

In the present invention, since the heat-receiving plate, the plurality of boards, and the heat-radiating plate are diffusion-bonded, there is no problem even when a heat source is connected to the heat-receiving plate by reflow after the injection of the working fluid. In other words, it is possible to secure a strength sufficient to endure a tension stress applied to the phase-change-type heat spreader at a time the working fluid evaporates inside the flow path during reflow and an internal pressure of the flow path increases.

When the strength is small, the working fluid needs to be injected into the flow paths after the reflow process. Specifically, in the reflow process, since the temperature of the heat-receiving plate, the plurality of boards, and the like is increased by soldering and the like, if the working fluid is in the flow paths at that time, an internal pressure increases by the evaporation of the working fluid to thus break the phase-change-type heat spreader.

There are cases where the reflow process and the production process of the phase-change-type heat spreader are carried out at different places (e.g., different factories). Thus, when the working fluid is injected after the reflow, the phase-change-type heat spreader needs to be reciprocated between the factories, for example, to thus cause problems on costs, labor of workers, times, and particles generated during the reciprocation between the factories. According to the present invention, it becomes possible to perform reflow after the phase-change-type heat spreader is completed. Therefore, in the present invention, the problems as described above can be solved, and product reliability can thus be enhanced.

EFFECT OF THE INVENTION

As described above, according to the phase-change-type heat spreader of the present invention, a thermal efficiency by a phase change can be improved and a thermal resistance can be lowered.

According to the method of producing a phase-change-type heat spreader of the present invention, production can be made easier and reliability can be improved.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view showing a phase-change-type heat spreader according to an embodiment of the present invention. FIG. 2 is a side view of a phase-change-type heat spreader 100 in a state where a heat source is connected to the phase-change-type heat spreader 100. FIG. 3 is an exploded perspective view of the phase-change-type heat spreader 100.

As shown in FIG. 2, the phase-change-type heat spreader 100 includes a heat-receiving plate 500, a heat-radiating plate 200 opposed to the heat-receiving plate 500, and a plurality of flow-path boards 600 that are laminated between the heat-receiving plate 500 and the heat-radiating plate 200 and constitute a flow path of a refrigerant (working fluid).

A heat source 50 is thermally connected to a surface 501 of the heat-receiving plate 500. Examples of the heat source 50 include electronic components such as an IC (Integrated Circuit) and a resistor and other devices that radiate heat.

As shown in FIG. 3, the plurality of flow-path boards 600 include a plurality of capillary boards (first board, flow-path structure, first structural member) 400 that constitute a flow path that is capable of causing a liquid-phase refrigerant (hereinafter, referred to as liquid refrigerant) to circulate by a capillary force. Moreover, the plurality of flow-path boards 600 include a plurality of vapor-phase boards 300 (second board, second structural member) that constitute a part of a vapor-phase flow path for mainly causing an evaporated vapor-phase refrigerant (hereinafter, referred to as vapor refrigerant) to circulate.

The number of capillary boards 400 is, for example, 10 to 30, typically 20. However, the number of capillary boards 400 can be changed as appropriate based on an amount of heat radiated from the heat source 50 thermally connected to the heat-receiving plate 500, and is not limited to 10 to 30. The number of vapor-phase boards 300 is, for example, 1 to 20, typically 8. The number of vapor-phase boards 300 can also be changed as appropriate as in the case of the capillary boards 400 and is not limited to 1 to 20.

FIG. 4 is a cross-sectional diagram showing a part of a cross section taken along the line A-A of FIG. 1. In FIG. 4, for brevity of description, an example in which the capillary boards 400 and the vapor-phase boards 300 are provided 4 each (401 to 404, 301 to 304) is shown.

In FIG. 4, the heat-receiving plate 500, the plurality of capillary boards 400 (hereinafter, referred to as capillary board group 410), the plurality of vapor-phase boards 300 (hereinafter, referred to as vapor-phase board group 310), and the heat-radiating plate 200 are laminated in the stated order from the bottom. Of the capillary board group 410, the capillary board 404 at the bottom is bonded to the heat-receiving plate 500, and the capillary board 401 at the top is bonded to the vapor-phase board 304 at the bottom. The vapor-phase board 301 at the top is bonded to the heat-radiating plate 200.

In descriptions below, of the capillary boards 401 to 404, an arbitrary one of the capillary boards 400 will be described as a representative regarding parts having the same structure, in the case of which that one will be referred to as “capillary board 400”. Similarly, of the vapor-phase boards 301 to 304, an arbitrary one of the vapor-phase boards 300 will be described, in the case of which that one will be referred to as “vapor-phase board 300”.

FIG. 5 is a perspective view showing a part of the heat-receiving plate 500 on an inner side. A plurality of grooves 505 are formed on an inner side 509 of the heat-receiving plate 500. A depth of the grooves 505 is 10 to 50 μm, typically bout 20 μm, though not limited to this range. The depth of the grooves 505 is set to a value that enables an appropriate capillary force to act on the liquid refrigerant.

By forming the plurality of grooves 505, a plurality of ribs 506 are formed between the grooves 505. Regarding the formation of such ribs 506, the same holds true for the capillary board 400, the vapor-phase board 300, and the heat-radiating plate 200 to be described later.

On the heat-receiving plate 500, an injection path and an inlet for the refrigerant (both of which are not shown) are formed. The injection path and the inlet may be formed on the heat-radiating plate 200.

FIG. 6 is a perspective view showing a part of the two laminated capillary boards 400, for example. FIG. 7 is a plan view showing a part of the capillary board group 410. FIG. 8 is a cross-sectional diagram taken along the line B-B of FIG. 7. FIG. 9 is a plan view of the entire capillary board 400.

A plurality of grooves (first grooves) 405 are formed on a surface of the capillary board 400. A depth of the grooves 405 is 10 to 50 μm, typically about 20 μm, though not limited to this range. The depth of the grooves 405 is set to a value that enables an appropriate capillary force to act on the liquid refrigerant.

It should be noted that in the capillary board 400 shown in FIG. 9, to help understand the figure, the grooves 405 and the like are illustrated in large scales with respect to a size of the entire capillary board 400. The same holds true for FIGS. 11 and 12 to be described later.

The capillary boards 401 to 404 are laminated while each being rotated 90 degrees within an X-Y plane so that the grooves 405 thereof extend in mutually-orthogonal directions. On wall surfaces 430 (see FIGS. 7 and 8) constituting the grooves 405 of the capillary board 400, a plurality of openings 408 penetrating the capillary board 400 are formed along a longitudinal direction of the grooves 405 (e.g., X direction in FIG. 7). The wall surfaces 430 constituting the grooves 405 are each constituted of side surfaces 431 of the ribs and a floor surface 432, and the plurality of openings 408 are formed on the floor surfaces 432.

For example, focusing on the capillary board 401 and the capillary board 402 adjacent thereto, the capillary board 401 and the capillary board 402 are bonded while being arranged relatively so that the grooves 405 of the capillary board 401 and the grooves 405 of the capillary board 402 are in communication via the openings 408 of the capillary board 401.

In other words, the capillary board 401 and the capillary board 402 are bonded while being arranged relatively so that ribs 406 of the capillary board 402 do not block the openings 408 of the capillary board 401 and a back surface of the capillary board 401 is bonded to the ribs 406 of the capillary board 402. The same holds true for the relative positions of the capillary board 402 and the capillary board 403, and the capillary board 403 and the capillary board 404.

The openings 408 function as a part of a vapor-phase flow path through which a vapor refrigerant that has been evaporated by heat received by the heat-receiving plate 500 circulates.

The openings 408 of those layers are arranged in a direction in which the flow-path boards 600 are laminated (Z direction), that is, in a direction in which opening surfaces are opposed to one another. With this structure, a flow-path resistance at a time the vapor refrigerant circulates via the openings 408 arranged in the Z direction becomes smaller, and a thermal efficiency is improved. However, the openings 408 do not always need to be arranged in the Z direction and may alternatively be arranged such that the openings 408 of a certain layer are slightly deviated in the Y direction or the X direction from the openings 408 of a layer adjacent thereto.

Focusing again on the capillary board 401 and the capillary board 402 adjacent thereto, as shown in FIG. 8, areas surrounded by the wall surfaces 430 constituting the grooves 405 of the capillary board 402 and ceiling surfaces 433 on a back-surface side of the capillary board 401 that are opposed to the floor surfaces 432 of the wall surfaces 430 mainly function as a flow path for the liquid refrigerant that uses a capillary force. It should be noted that since the openings 408 are formed on the floor surfaces 432 and the ceiling surfaces 433, areas penetrated by the openings 408 in the Z direction function as a flow path for the vapor refrigerant.

More specifically, a capillary force most-strongly acts on the liquid refrigerant at a boundary between the side surfaces 431 and the floor surfaces 432 and a boundary between the side surfaces 431 and the ceiling surfaces 433, in the wall surfaces 430 in particular. As a result, as shown in FIG. 7, the liquid refrigerant passes areas 440 avoiding the openings 408. It should be noted that the “wall surfaces” conceptually include the ceiling surfaces 433 in addition to the side surfaces 431 and the floor surfaces 432.

For example, when the grooves 405 of the capillary board 401 function as a first flow-path layer, the grooves 405 of the capillary board 402 adjacent thereto function as a second flow-path layer.

As shown in FIG. 7, a width b of the grooves 405 is 100 to 200 μm, a width c of the ribs 406 is 50 to 100 μm, and a diameter d of the openings 408 is 50 to 100 μm. However, the values are not limited to those ranges and can be changed as appropriate according to a heat quantity and the like of the heat source 50.

Although the openings 408 are typically circular, a shape thereof may be any shape including an oval, an elongate hole, and a polygon.

FIG. 10 is a perspective view showing a part of two laminated vapor-phase boards 300, for example. FIG. 10 will be described while mainly focusing on the vapor-phase boards 301 and 302.

The vapor-phase boards 300 are typically constituted of two types of boards. FIG. 11 is a plan view showing the entire vapor-phase board 301. FIG. 12 is a plan view showing the entire vapor-phase board 302. The vapor-phase boards 301 and 302 are common in that a plurality of grooves (second grooves) 305 penetrating in the Z direction are provided. A depth of the grooves 305 is 50 to 150 μm, typically about 100 μm, though not limited to this range. The depth of the grooves 305 is set to a value with which the vapor refrigerant can be circulated and condensed appropriately.

Due to the plurality of grooves 305 being formed on a single vapor-phase board 300, a plurality of ribs 306 are formed. As shown in FIG. 10, the vapor-phase board 301 and the vapor-phase board 302 are arranged while being deviated 90 degrees in a rotational direction within the X-Y plane so that a direction in which the grooves 305 of the vapor-phase board 301 extend and a direction in which the grooves 305 of the vapor-phase board 302 adjacent to the vapor-phase board 301 extend become orthogonal. The vapor-phase boards 303 and 304 also have the same structure, and the vapor-phase boards 301 to 304 are arranged while being sequentially deviated 90 degrees from one another.

The grooves 305 of the vapor-phase boards 301 to 304 are areas through which mainly the vapor refrigerant circulates, and the grooves 305 function as a condensation area as a part of the vapor-phase flow path.

As shown in FIG. 12, the vapor-phase board 302 includes, around the area in which the grooves 305 are formed, an area in which return holes 308 (return flow path) for the condensed and liquified liquid refrigerant to return to the grooves 405 of the capillary boards 400 are formed. The vapor-phase board 301 does not include the return holes 308 and provided with the grooves 305 at a position adjacent to the return holes 308 of the vapor-phase board 302 in the Z direction.

A diameter of the return holes 308 is set to be about 50 to 150 μm, but the diameter is not limited to this range and can be changed as appropriate. The diameter of the return holes 308 is set to a value that enables a capillary force to act on the liquid refrigerant at a time the vapor refrigerant is condensed to become the liquid refrigerant.

The vapor-phase board 301 that does not include the return holes 308 and the vapor-phase board 302 including them are paired up as described above, and a plurality of those pairs are typically laminated in this embodiment. In other words, in FIG. 4, the vapor-phase boards 301 and 303 are boards that do not include the return holes 308, and the vapor-phase boards 302 and 304 are boards that include the return holes 308.

A width of the area in which the return holes 308 are formed is about 5 to 10 mm, but the width is not limited to this range and can be changed as appropriate.

It should be noted that only the plurality of vapor-phase boards 301 not including the return holes 308 may be laminated to thus constitute the vapor-phase board group 310, or only the plurality of vapor-phase boards 302 including the return holes 308 may be laminated to thus constitute the vapor-phase board group 310. Alternatively, the vapor-phase boards 300 disposed closer to the heat-radiating plate 200 may be the plurality of vapor-phase boards 301 that do not include the return holes 308, and the vapor-phase boards 300 disposed closer to the capillary board 400 may be the plurality of vapor-phase boards 302 that include the return holes 308. Alternatively, the plurality of vapor-phase boards 301 and the plurality of vapor-phase boards 302 may be laminated randomly.

For example, when the grooves 305 of the vapor-phase board 302 function as the first flow-path layer, the grooves 305 of the vapor-phase board 302 adjacent thereto function as the second flow-path layer.

As shown in FIG. 4, the heat-radiating plate 200 includes a plurality of grooves 205 on an inner side like the heat-receiving plate 500. The plurality of grooves 205 have the same function as the grooves 305 of the vapor-phase boards 300 and only need to be formed in the same size as the grooves 305.

The heat-receiving plate 500, the capillary board group 410, the vapor-phase board group 310, and the heat-radiating plate 200 are laminated such that a columnar structure (area surrounded by broken line 630) is formed in the Z direction by the ribs 506, 406, 306, and 206 of the heat-receiving plate 500, the capillary board group 410, the vapor-phase board group 310, and the heat-radiating plate 200, respectively. By thus forming a plurality of columnar structures 630, it is possible to secure a strength sufficient to endure a compression stress externally applied to the phase-change-type heat spreader 100.

Further, by bonding the heat-receiving plate 500, the capillary board group 410, the vapor-phase board group 310, and the heat-radiating plate 200 by diffusion bonding, a strength sufficient to endure a tension stress generated inside the phase-change-type heat spreader 100 as will be described later can also be obtained.

The grooves 505, 405, 305, and 205, the openings 408, the injection path for the refrigerant, and the like structured as described above are typically formed by an MEMS (Micro Electro Mechanical Systems) technique such as photolithography and etching. However, other processing methods such as laser processing may be used instead.

As shown in FIGS. 3, 9, 11, and 12, the heat-receiving plate 500, the flow-path boards 600, and the heat-radiating plate 200 include frame portions 507, 407, 307, and 207 in which the grooves 505, 405, 305, and 205 are not formed. The frame portions 507, 407, 307, and 207 are bonded. In other words, a container of the phase-change-type heat spreader 100 is formed by the heat-receiving plate 500, the heat-radiating plate 200, and the frame portions 507, 407, 307, and 207.

For example, as shown in FIG. 9, a width f of each of the frame portions 507, 407, 307, and 207 is several mm, but can be changed as appropriate. The width f is set to an appropriate value based on a strength as the container, a ratio of the flow-path portion to the phase-change-type heat spreader 100 within the X-Y plane, a heat quantity of the heat source 50, or the like.

The heat-receiving plate 500, the heat-radiating plate 200, and the flow-path boards 600 are typically formed of a metal material. Examples of the metal material include copper, stainless steel, and aluminum, through not limited thereto. In addition to metal, a material having high heat conductivity such as carbon may be used. The heat-receiving plate 500, the heat-radiating plate 200, and the flow-path boards 600 may all be formed of different materials, or two of those may be formed of the same material.

Examples of the refrigerant include pure water, ethanol, methanol, acetone, isopropyl alcohol, hydrochlorofluorocarbon, and ammonia, though not limited thereto.

As shown in FIG. 1, a length e of one side of the phase-change-type heat spreader 100 is, for example, 30 to 50 mm, though not limited to this range.

The heat-receiving plate 500, the plurality of flow-path boards 600, and the heat-radiating plate 200 may be bonded by brazing, that is, welding, or an adhesive may be used for the bonding depending on the material. Alternatively, the diffusion bonding described above may be used for the bonding. The plurality of capillary boards 400 or the plurality of vapor-phase boards 300 also only need to be bonded in the same manner.

An operation of the phase-change-type heat spreader 100 structured as described above will be described. FIG. 13 is a schematic diagram for explaining the operation.

When heat is generated by the heat source 50, the heat is received by the heat-receiving plate 500. As a result, the liquid refrigerant collected in the grooves 405 of the capillary board group 410 by a capillary force is boiled to thus evaporate. A part of the vapor refrigerant circulates inside the grooves 405, but most of the vapor refrigerant circulates so as to move toward the heat-radiating plate 200 via the openings 408 and circulates through the grooves 305 of the vapor-phase board group 310. By the circulation of the vapor refrigerant in the grooves 305, the heat is diffused and the vapor refrigerant is condensed. Accordingly, the heat is mainly radiated from the heat-radiating plate 200. The condensed vapor refrigerant returns to the grooves 405 of the capillary board group 410 via the return holes 308 using the capillary force. By repeating the operations as described above, heat from the heat source 50 is diffused by the phase-change-type heat spreader 100.

Areas of the operations indicated by the arrows in FIG. 13 each show an indication or a reference to some extent, and because the operational areas shift more or less depending on the heat quantity of the heat source 50, the operational areas are not clearly sectioned from one another.

It should be noted that in some cases, a member for radiating heat, such as a heat sink (not shown), is thermally connected to a surface of the heat-radiating plate 200 of the phase-change-type heat spreader 100. In this case, heat diffused by the phase-change-type heat spreader 100 is transferred to the heat sink to be radiated therefrom.

As described above, the phase-change-type heat spreader 100 of this embodiment presupposes mixing of the vapor-phase working fluid and the liquid-phase working fluid and is thus a device that has been made based on a basic idea of controlling circulation directions of the working liquids.

Specifically, the liquid refrigerant circulates through the plurality of grooves 405 formed within the X-Y plane, whereas most of the vapor refrigerant circulates in the Z direction via the openings 408 having a small flow-path resistance. Since the liquid refrigerant that circulates through the grooves 405 is collected mainly at a center of the side surfaces 431 of the wall surfaces 430, it is possible to prevent the vapor refrigerant from inhibiting the circulation of the liquid refrigerant. As a result, a thermal efficiency by a phase change can be improved, and a thermal resistance can be lowered.

FIG. 14 is a graph showing a result of simulating cooling performance of the phase-change-type heat spreader 100 of this embodiment.

The abscissa axis represents a heat quantity of the heat source 50 input to the phase-change-type heat spreader 100, and the ordinate axis represents a thermal resistance. In the simulation, as a scale of the phase-change-type heat spreader 100, b, c, and d in FIG. 7 were set to 160 μm, 80 μm, and 80 μm, respectively, a in FIG. 8 was set to 20 μm, the thickness of the phase-change-type heat spreader 100 in the Z direction was set to 2.6 mm, and e in FIG. 1 was set to 40 μm (square). Copper was used as the material of the heat-receiving plate 500, the heat-radiating plate 200, and the flow-path boards 600. Pure water was used as the refrigerant.

A device as a target for comparison is a 40 mm×40 mm square-shaped solid-type copper heat spreader that has a thickness of 2.6 mm.

As can be seen from the graph, in the phase-change-type heat spreader 100, with an input heat quantity of 70 W, for example, the thermal resistance decreased 20% as compared to the solid-type copper, which is a significant improvement.

FIGS. 15(A) and 15(B) are a diagram and a graph showing a simulation result of a thermal diffusion operation of the solid-type heat spreader used in the experiment of FIG. 14. FIGS. 16(A) and 16(B) are a diagram and a graph showing a simulation result of a thermal diffusion operation of the phase-change-type heat spreader 100 used in the experiment of FIG. 14. Used as the heat source 50 was a 20 mm×20 mm square-shaped IC, and an input heat quantity thereof was 100 W. In FIGS. 15(A) and 16(A), a center point of the cross is a center of the phase-change-type heat spreader 100 and a center of the heat source 50.

It can be seen from the graphs that a temperature gradient of thermal diffusion by the phase-change-type heat spreader 100 is more gradual than the solid-type heat spreader, a center temperature is low, and a thermal diffusion operation is high.

FIG. 17 is a graph showing a relationship between a capillary force generated by the grooves 405 of the capillary boards 400 and a flow-path resistance. In this example, a material of the capillary boards 400 is copper, and the refrigerant is pure water. The capillary force and the flow-path resistance are in a tradeoff relationship. Therefore, it is necessary to adjust a balance between those two. The abscissa axis in the graph represents a height of a capillary (depth of groove 405), and the abscissa axis represents a pressure applied to the refrigerant by the capillary force or the flow-path resistance.

It is desirable for the flow-path resistance to be extremely small and the capillary force to be extremely large. Thus, a height of the capillary with a greatest differential pressure becomes an optimal value, which is about 20 μm in this example.

If the height of the capillary is smaller than 10 μm, a circulation amount of the liquid refrigerant is reduced to thus lower a thermal efficiency. If the height of the capillary is larger than 50 μm, a desired capillary force does not act on the working fluid, and the thermal efficiency is thus lowered.

FIG. 24 are diagrams showing experimental examples in which the inventors of the present invention have used the phase-change-type heat spreader 100 of this embodiment like a well-known heat-pipe type (e.g., planar heat pipe). The phase-change-type heat spreader 100 and the heat pipe are common in the point of using a capillary force and phase-change latent heat in principle. A different point is that the phase-change-type heat spreader 100 is connected to the heat source at mainly a center thereof and heat is diffused in a direction of a main surface of the phase-change-type heat spreader 100, whereas the heat pipe has the heat source being physically apart from the heat-radiating side and heat is carried to the heat-radiating side from the heat source.

Therefore, the inventors of the present invention have conducted the experiments from a viewpoint that since separation of a vapor phase and a liquid phase and an enforcement of a capillary force are more developed in the phase-change-type heat spreader 100, it may be possible to use the phase-change-type heat spreader 100 as the heat-pipe type.

The phase-change-type heat spreader used in the experiments was the 40 mm×40 mm square-shaped phase-change-type heat spreader 100 described above. Moreover, a water-cooling jacket 11 was used on the heat-radiating side.

FIG. 24(A) shows an experimental example in bottom heat in which the heat source 50 is attached to a lower portion of the phase-change-type heat spreader 100. FIG. 24(B) shows an experimental example in top heat in which the heat source 50 is attached to an upper portion of the phase-change-type heat spreader 100. In other words, FIGS. 24(A) and 24(B) are opposite and take into account an effect of gravity that acts on the working fluid. The working fluid is apt to accumulate at a lower portion by its own weight. Thus, in general, the temperature of the heat source 50 is apt to decrease more in the bottom heat than the top heat.

As shown in those figures, a side of the phase-change-type heat spreader 100 on the other side of the heat source 50 is connected with a water-cooling jacket base 12 via a heat-conductive grease 13. A distance from an end portion of the heat source 50 to a portion at which the water-cooling jacket base 12 is connected is 10 mm.

FIG. 25 is a graph showing a relationship between an input heat quantity and a temperature of the heat source 50 in the case of the phase-change-type heat spreader 100 and the case where a solid-type copper plate is used in place of the phase-change-type heat spreader 100, in the experiments shown in FIG. 24. The copper plate is of the same size as the phase-change-type spreader (also having same thickness of 2.6 mm).

It can be seen from the graph that although the distance from the end portion of the heat source 50 to the part at which the water-cooling jacket base 12 is connected (10 mm) is short, the phase-change-type heat spreader 100 is sufficiently functioning as a heat pipe without causing dryout. In the case of the phase-change-type heat spreader 100, the temperature of the heat source 50 at an input heat quantity of 50 W is a value that is about 10° C. lower than that in the case of the copper plate in both of the top heat and the bottom heat.

FIG. 18 is a cross-sectional diagram schematically showing a phase-change-type heat spreader according to another embodiment of the present invention. FIG. 19 is a plan view of a phase-change-type heat spreader 150 shown in FIG. 18. In descriptions below, descriptions on components, functions, and the like that are the same as those of the phase-change-type heat spreader 150 according to the embodiment shown in FIG. 1 and the like will be simplified or omitted, and different points will mainly be described.

On the heat-receiving plate 500, two inlets 526 for a refrigerant and two injection paths 527 that are respectively in communication therewith are formed, for example. It should be noted that the injection paths 527 and the inlets 526 are formed by bonding, after grooves (grooves for injection paths 527) and openings (openings for inlets 526) are formed on one of the two boards, the two boards together to thus form the heat-receiving plate 500. The injection paths 527 are in communication with the grooves 405 of the capillary boards 400. The inlet 526 and the injection path 527 may be provided one each. It should be noted that a part in slashes in FIG. 19 indicates a part where a flow path of a refrigerant is formed by the flow-path boards 600.

The injection paths 527 are formed linearly, for example, and predetermined areas on the line become press areas 540 for blocking the injection paths 527 by applying a pressure thereto. In other words, the press areas 540 are swaging areas. Inside the phase-change-type heat spreader 150, that is, in an area where the flow-path boards 600 are disposed, columnar portions 603 extending in the Z direction from the heat-receiving plate 500 to the heat-radiating plate 200 are formed at positions corresponding to the swaging areas.

The columnar portions 603 only need to be formed by laminating columnar ribs formed in each of the heat-receiving plate 500, the capillary boards 400, the vapor-phase boards 300, and the heat-radiating plate 200. A width (or diameter) of the columnar portions 603 is set as appropriate to a width with which the flow path constituted of the flow-path boards 600 (hereinafter, referred to as internal flow path) is not blocked by a pressing force during swaging.

FIG. 20 are schematic diagrams showing a method of injecting a refrigerant into the phase-change-type heat spreader 150 in sequence.

As shown in FIG. 20(A), for example, the internal flow path is pressure-reduced via the inlet 526 and the injection path 527, and a refrigerant is injected into the internal flow path by a dispenser (not shown) via the inlet 526 and the injection path 527.

As shown in FIG. 20(B), the press area 540 is pressed to thus block the injection path 527 (temporary sealing). After that, the internal flow path is pressure-reduced via another injection path 527 and inlet 526, and at a point the internal flow path has reached a target pressure, the press area 540 is pressed to thus block the injection path 527 as shown in FIG. 20(B) (temporary sealing).

Subsequently, as shown in FIG. 20(C), on a side closer to the inlet 526 than the press area 540, the injection path 527 is blocked by, for example, laser welding (actual sealing). As a result, the inside of the phase-change-type heat spreader 150 is sealed.

As described above, since the phase-change-type heat spreader 150 includes the columnar portions 603 at positions corresponding to the press areas 540, the internal flow path can be prevented from being dented and blocked by a pressing force during swaging.

It is also possible to structure the phase-change-type heat spreader 150 such that the internal flow path is not formed at a position corresponding to the injection paths 527. In other words, a dedicated press area 540 may be provided at a position not corresponding to the internal flow path. However, since the internal flow path is not provided at the position corresponding to such a dedicated press area 540, the position corresponding to the dedicated press area 540 is an area with a low thermal diffusion function.

According to the phase-change-type heat spreader 150 of this embodiment, since the internal flow path is formed around the columnar portions 603, a thermal diffusion efficiency can be improved on almost the entire surface of the phase-change-type heat spreader 150.

It should be noted that the injection paths 527 and the inlets 526 may be formed on the heat-radiating plate 200.

Next, an embodiment of a method of producing the phase-change-type heat spreader 150 (or phase-change-type heat spreader 150) will be described. FIG. 21 is a flowchart showing the production method.

A plurality of boards are prepared, and the grooves 505, 405, 305, and 205, the openings 408, and the like are formed on those boards (Step 101). Accordingly, the heat-receiving plate 500, the plurality of flow-path boards 600, and the heat-radiating plate 200 are formed.

The heat-receiving plate 500, the plurality of flow-path boards 600, and the heat-radiating plate 200 are laminated so as to interpose the plurality of flow-path boards 600 between the heat-receiving plate 500 and the heat-radiating plate 200 and diffusion-bonded thereafter (Step 102). At the time of lamination, accurate positioning of the boards is carried out. Since diffusion bonding has a metallic bonding operation, a strength or rigidity of the phase-change-type heat spreader 150 can be enhanced.

As shown in FIGS. 20(A) to 20(C), the refrigerant is injected into the internal flow path and the injection paths are sealed (Step 103). Accordingly, the phase-change-type heat spreader 150 is completed.

After that, the heat source 50 is mounted on the heat-receiving plate 500 (Step 104). In a case where the heat source 50 is an IC, this process may be carried out by a reflow process such as soldering. In the reflow process, the temperature of the heat-receiving plate 500 or the entire phase-change-type heat spreader 150 becomes as high as 230 to 240° C. due to soldering and the like. In such an environment, although an internal pressure increases by an evaporation of the refrigerant, since diffusion bonding is performed in Step 102, a strength and rigidity sufficient to endure a tension stress caused by the internal pressure can be secured.

There are cases where the reflow process and the production process of the phase-change-type heat spreader 150 are carried out at different places (e.g., different factories). Thus, when the working fluid is injected after the reflow, the phase-change-type heat spreader 150 needs to be reciprocated between the factories, for example, to thus cause problems on costs, labor of workers, times, and particles generated during the reciprocation between the factories.

According to the production method shown in FIG. 21, it becomes possible to perform reflow after the phase-change-type heat spreader 150 is completed, with the result that the problems described above can be solved.

FIG. 22 is a schematic diagram showing another embodiment of the phase-change-type heat spreader 100 or 150. In FIG. 22, ribs 416 of the plurality of capillary boards 400 include a plurality of columnar portions 417, for example. Pitches of the plurality of columnar portions 417, the number thereof, sizes of the columnar portions 417, and the like can be set as appropriate. The shape is not limited to the columnar shape and may be an oval, a square, or other shapes.

The plurality of capillary boards 400 are bonded so that the columnar portions 417 of those plurality of capillary boards 400 are bonded while overlapping one another in the Z direction. The same holds true for the bonding of the heat-receiving plate 500 and the capillary boards 400, the bonding of the capillary boards 400 and the vapor-phase boards 300, and the bonding of the vapor-phase boards 300 and the heat-radiating plate 200.

With such a structure, a bonding area can be increased without effecting the internal flow path, and a strength or rigidity with respect to an external compression stress or an internal tension stress with respect to the phase-change-type heat spreader 150 can be enhanced.

FIG. 23 is a perspective view showing a desktop PC as an electronic apparatus including the phase-change-type heat spreader 100. A circuit board 22 is disposed inside a casing 21 of a PC 20, and a CPU 23 is mounted on the circuit board 22, for example. The phase-change-type heat spreader 100 (or 150) is thermally connected to the CPU 23, and a heat sink (not shown) is thermally connected to the phase-change-type heat spreader 100.

An embodiment of the present invention is not limited to the above embodiments, and various other embodiments may also be adopted.

A planar shape of the phase-change-type heat spreader 150 has been a quadrangle or a square. However, the planar shape may be a circle, an oval, a polygon, or other arbitrary shapes.

The shapes and the like of the grooves 505, 405, 305, and 205, the wall surfaces 430, the ribs 506, 406, 306, and 206, and the frame portions 507, 407, 306, and 207 can be changed as appropriate.

The PC has been exemplified as the electronic apparatus in FIG. 23. However, the present invention is not limited thereto, and other examples of the electronic apparatus include a PDA (Personal Digital Assistance), an electronic dictionary, a camera, a display apparatus, audiovisual equipment, a projector, a cellular phone, game equipment, car navigation equipment, robot equipment, a laser generation apparatus, and other electrical appliances.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] A plan view of a phase-change-type heat spreader according to an embodiment of the present invention.

[FIG. 2] A side view of the phase-change-type heat spreader in a state where a heat source is connected to the phase-change-type heat spreader.

[FIG. 3] An exploded perspective view of the phase-change-type heat spreader.

[FIG. 4] A cross-sectional diagram showing a part of the cross section taken along the line A-A of FIG. 1.

[FIG. 5] A perspective view showing a part of a heat-receiving plate on an inner side.

[FIG. 6] A perspective view showing a part of two laminated capillary boards.

[FIG. 7] A plan view showing a part of a capillary board group.

[FIG. 8] A cross-sectional diagram taken along the line B-B of FIG. 7.

[FIG. 9] A plan view of the entire capillary board.

[FIG. 10] A perspective view showing a part of two laminated vapor-phase boards.

[FIG. 11] A plan view of the entire vapor-phase board.

[FIG. 12] A plan view of the entire vapor-phase board that is to become a pair with the vapor-phase board shown in FIG. 11.

[FIG. 13] A schematic diagram for explaining an operation of the phase-change-type heat spreader.

[FIG. 14] A graph showing a result of simulating cooling performance of the phase-change-type heat spreader according to this embodiment.

[FIG. 15] A diagram and a graph showing a simulation result of a thermal diffusion operation of a solid-type heat spreader used in the experiment of FIG. 14.

[FIG. 16] A graph showing a simulation result of a thermal diffusion operation of the phase-change-type heat spreader used in the experiment of FIG. 14.

[FIG. 17] A graph showing a relationship between a capillary force generated by grooves of the capillary board and a flow-path resistance.

[FIG. 18] A cross-sectional diagram schematically showing a phase-change-type heat spreader according to another embodiment of the present invention.

[FIG. 19] A plan view of the phase-change-type heat spreader shown in FIG. 18.

[FIG. 20] Schematic diagrams showing a method of injecting a refrigerant into the phase-change-type heat spreader in sequence.

[FIG. 21] A flowchart showing an embodiment of a method of producing a phase-change-type heat spreader.

[FIG. 22] A schematic diagram showing another embodiment of ribs of the phase-change-type heat spreader.

[FIG. 23] A perspective view of a laptop PC as an electronic apparatus including the phase-change-type heat spreader.

[FIG. 24] Diagrams showing experimental examples in which the inventors of the present invention have used the phase-change-type heat spreader of this embodiment as a heat pipe type (e.g., planar heat pipe), (A) showing an experimental example in bottom heat, (B) showing an experimental example in top heat.

[FIG. 25] A graph showing a relationship between an input heat quantity and a temperature of a heat source in the case of the phase-change-type heat spreader and a case where a solid-type copper plate is used in place of the phase-change-type heat spreader, in the experiments shown in FIG. 24.

DESCRIPTION OF REFERENCE NUMERALS

-   50 heat source -   100, 150 phase-change-type heat spreader -   150 phase-change-type heat spreader -   200 heat-radiating plate -   205, 305, 405, 505 groove -   300, 301, 302, 303, 304 vapor-phase board -   206, 306, 406, 416, 506 rib -   308 return hole -   400, 401, 402, 403, 404 capillary board -   401 capillary board -   408 opening -   430 wall surface -   500 heat-receiving plate -   526 inlet -   527 injection path -   540 press area -   603 columnar portion 

1. A phase-change-type heat spreader to diffuse heat using a phase change of a working fluid, the phase-change-type heat spreader comprising: a container including a heat-receiving side and a heat-radiating side opposed to the heat-receiving side; a plurality of flow paths provided in the container and laminated in a direction extending from the heat-receiving side to the heat-radiating side, each of the plurality of flow paths including a wall surface to cause the working fluid in a liquid phase to circulate by a capillary force; and a vapor-phase flow path, including an opening, to cause the working fluid in a vapor phase evaporated by heat received on the heat-receiving side to circulate so that the working fluid in the vapor phase moves toward the heat-radiating side via the opening, the opening penetrating the wall surface so that the plurality of flow paths are brought in communication with one another.
 2. The phase-change-type heat spreader according to claim 1, wherein the vapor-phase flow path includes a condensation area to condense the working fluid in the vapor phase, the condensation area being interposed between the heat-radiating side and the plurality of flow paths and being in communication with the plurality of flow paths via the opening.
 3. The phase-change-type heat spreader according to claim 2, further comprising a return flow path through which to return the working fluid in the liquid phase, that has been condensed in the condensation area, to the plurality of flow paths.
 4. The phase-change-type heat spreader according to claim 2, wherein the condensation area includes: a first flow-path layer including a plurality of first condensation flow paths to cause the working fluid to circulate in a first direction, and a second flow-path layer including a plurality of second condensation flow paths to cause the working fluid to circulate in a second direction different from the first direction and are in communication with the plurality of first condensation flow paths, the second flow-path layer being a layer different from the first flow-path layer in the direction extending from the heat-receiving side to the heat-radiating side.
 5. The phase-change-type heat spreader according to claim 1, wherein the plurality of flow paths include a first flow-path layer including a plurality of first flow paths to cause the working fluid to circulate in a first direction, and a second flow-path layer that includes a second flow path to cause the working fluid to circulate in a second direction different from the first direction and that is a layer different from the first flow-path layer in the direction extending from the heat-receiving side to the heat-radiating side.
 6. The phase-change-type heat spreader according to claim 1, wherein the opening of the vapor-phase flow path is one of a plurality of openings and the plurality of openings are arranged in the direction in which the plurality of flow paths are laminated.
 7. The phase-change-type heat spreader according to claim 1, wherein the container includes, on the heat-receiving side, an inlet for the working fluid, an injection path that is in communication with at least one of the plurality of flow paths and the inlet, and a press area to which to apply a pressure on the heat-receiving side and to block the injection path after the working fluid is injected into the plurality of flow paths via the inlet and the injection path, wherein the phase-change-type heat spreader further comprises: a columnar portion erected in the direction in which the plurality of flow paths are laminated at a position corresponding to the press area.
 8. The phase-change-type heat spreader according to claim 1, wherein the container includes, on the heat-radiating side, an inlet for the working fluid, an injection path that is in communication with at least one of the plurality of flow paths and the inlet, and a press area to which to apply a pressure on the heat-radiating side and to block the injection path after the working fluid is injected into the plurality of flow paths via the inlet and the injection path, wherein the phase-change-type heat spreader further comprises a columnar portion erected in the direction in which the plurality of flow paths are laminated at a position corresponding to the press area.
 9. The phase-change-type heat spreader according to claim 1, wherein a height of the plurality of flow paths in the direction in which the plurality of flow paths are laminated is 10 to 50 μm.
 10. The phase-change-type heat spreader according to claim 1, further comprising: a first structural member constituting the plurality of flow paths; and a second structural member constituting the vapor-phase flow path, wherein at least one of the container, the first structural member, and the second structural member is formed of copper.
 11. A phase-change-type heat spreader to diffuse heat using a phase change of a working fluid, the phase-change-type heat spreader comprising: a heat-receiving plate; a heat-radiating plate opposed to the heat-receiving plate; a plurality of first boards that each include a first groove to cause the working fluid in a liquid phase to circulate by a capillary force and an opening penetrating the first board so that the first grooves are brought in communication with one another so as to cause the working fluid in a vapor phase evaporated by heat received by the heat-receiving plate to circulate via the opening, the plurality of first boards being laminated in a direction extending from the heat-receiving plate to the heat-radiating plate; and a second board that includes a second groove to cause the working fluid in the vapor phase that has passed through the opening to circulate and that is provided between the heat-radiating plate and the plurality of first boards.
 12. The phase-change-type heat spreader according to claim 11, wherein the second groove penetrates the second board in the direction in which the plurality of first boards are laminated.
 13. The phase-change-type heat spreader according to claim 11, wherein the second board includes a return hole to return the working fluid in the liquid phase that has passed through the second groove to be condensed to the plurality of flow paths.
 14. The phase-change-type heat spreader according to claim 11, wherein the second board is one of a plurality of second boards, and at least one of the plurality of second boards includes a return hole to return the working fluid in the liquid phase that has passed through the second groove to be condensed to the plurality of flow paths.
 15. The phase-change-type heat spreader according to claim 11, wherein a depth of the first grooves is 10 to 50 μm.
 16. The phase-change-type heat spreader according to claim 11, wherein the plurality of first boards are each formed of copper.
 17. The phase-change-type heat spreader according to claim 16, wherein at least one of the heat-receiving plate, the heat-radiating plate, and the second board is formed of copper.
 18. A flow-path structure used in a phase-change-type heat spreader to diffuse heat received by a heat-receiving plate using a phase change of a working fluid and that includes the heat-receiving plate, a heat-radiating plate opposed to the heat-receiving plate, and a board including a groove that causes the working fluid in a vapor phase evaporated by the heat received by the heat-receiving plate to circulate, the flow-path structure being laminated between the heat-receiving plate and the board, the flow-path structure comprising: a plurality of ribs extending within a plane between the heat-receiving plate and the heat-radiating plate; and a wall surface, that includes an opening penetrating the flow-path structure, to cause the working fluid in the vapor phase to circulate so that the working fluid in the vapor phase moves toward the heat-radiating plate, and to cause the working fluid in a liquid phase to circulate by a capillary force, the wall surface being provided between the plurality of ribs.
 19. An electronic apparatus, comprising: a heat source; and a phase-change-type heat spreader including a working fluid, a container including a heat-receiving side to receive heat from the heat source and a heat-radiating side opposed to the heat-receiving side, a plurality of flow paths provided in the container and laminated in a direction extending from the heat-receiving side to the heat-radiating side, each of the plurality of flow paths including a wall surface that causes the working fluid in a liquid phase to circulate by a capillary force, and a vapor-phase flow path, including an opening, to cause the working fluid in a vapor phase evaporated by the heat received on the heat-receiving side to circulate so that the working fluid in the vapor phase moves toward the heat-radiating side via the opening, the opening penetrating the wall surface so that the plurality of flow paths are brought in communication with one another.
 20. A method of producing a phase-change-type heat spreader, the method comprising: laminating a heat-receiving plate, a plurality of boards each including a groove for causing a working fluid to circulate, and a heat-radiating plate such that the plurality of boards are interposed between the heat-receiving plate and the heat-radiating plate; diffusion-bonding the heat-receiving plate, the plurality of boards, and the heat-radiating plate that have been laminated to form a flow path of the working fluid that corresponds to the grooves; injecting the working fluid into the grooves via an injection path for the working fluid, the injection path being formed on the heat-receiving plate or the heat-radiating plate and in communication with the flow path; and sealing, after the injection of the working fluid, an inside of the flow path by blocking the injection path before connecting a heat source to the heat-receiving plate by reflow. 